LCD driver with adjustable contrast

Description

Field of the Invention:

[0001] This invention relates to a Liquid Crystal Display (LCD) driver that provides adjustable contrast independently of the multiplexing method.

Background of the Invention:

[0002] LIQUID CRYSTAL DISPLAYS (LCDs) are used for displaying messages. There are various methods to drive the LCD display. One method uses inbuilt hardware drivers/controllers to control the display of characters/graphics on the LCD. Such LCD modules are easier to interface but are expensive due to the inbuilt hardware drivers/controllers. Another method to drive an LCD display is through a dedicated Microcontroller which has an inbuilt hardware LCD driver to control the LCD display as well as the Contrast. Such a method is also relatively expensive.

[0003] US patent No. 4385294 describes an LCD display controller in which the LCD display is controlled by means of dedicated display drive circuitry. However, this display drive circuitry fails to work if the RMS voltage output of the circuitry is less than the LCD operating voltage. This arrangement is also relatively expensive to use.

[0004] The publication by Burgan et al "Liquid Crystal Display Digital Contrast Adjust", MOTOROLA TECHNICAL DEVELOPMENTS, MOTOROLA, INC. SCHAUMBURG, ILLINOIS, US, vol. 31, June 1997, pp. 80-83 discloses an LCD display driver for multiplex driving a LCD display according to the preamble of claim 1.

Summary of the Invention:

[0005] The object of present invention to provide an improved and cost effective system for driving an LCD display and providing adjustable contrast independently of multiplexing requirements.

[0006] Another object of this invention is to provide a solution that makes use of minimal hardware and thus provides a cost effective solution.

[0007] To achieve the said objectives the invention provides an LCD display driver providing adjustable contrast independently of multiplexing requirements according to claim 1.

[0008] Claim 8 claims a corresponding method for multiplex driving an LCD display.

[0009] The above method uses a standard microcontroller.

[0010] The biasing voltage is provided by using a resistor network across the COM signal line

Brief Description of the Accompanying Drawings:

[0011] The invention will now be explained with reference to the accompanying drawings:

Figure 1 shows the basic timing diagrams for a quadruplex multiplexer LCD display.

Figure 2 shows the timing diagram for a quadruplex LCD display driver according to this invention, in which the LCD voltage is decreased to adapt the RMS output voltage to low threshold voltage LCD display.

Figure 3 shows the timing diagram for a quadruplex LCD display driver according to this invention, in which the LCD voltage is increased to adapt to high threshold voltage LCD display

Figure 4 shows an implementation using a standard microcontroller.

Figure 5 shows a flowchart of the software for the implementation of figure 4.

Detailed Description:

[0012] Figure 1 shows the timing waveforms for a standard LCD display using a quadruplex multiplex method.

[0013] When a low RMS voltage is applied to an LCD, it is practically transparent. The LCD segment is inactive (OFF) if the RMS voltage is below the LCD threshold voltage and is active (ON) if the LCD RMS voltage is above the threshold voltage. The LCD threshold voltage depends on the properties of the liquid used in the LCD and the temperature. The optical contrast is defined by the difference in the transparency of an LCD segment that is ON (dark) and an LCD segment that is OFF (transparent). The optical contrast depends on the difference between the RMS voltage in the ON state (Von) and the RMS voltage in the OFF state (Voff). The larger the difference between Von and Voff, the greater is the optical contrast. The optical contrast depends as well on the difference between the on-state voltage Von and the LCD threshold voltage. If Von is below or close to the threshold voltage, the LCD is completely or almost transparent. Similarly, if Voff is close or above the threshold voltage, the LCD is completely dark.

[0014] To turn ON an LCD segment, there should be a voltage difference between the segment and common lines. With reference to the figure 1 that describes the general method to drive the Quadruplex LCD glass( four common lines), the Vrms( On) and Vrms( Off) of an LCD segment is calculated as -

[0015] Figures 2 & 3 show the timing diagrams for a similar quadruplex LCD display driven according to this invention.

[0016] Contrast is controlled by tuning the RMS voltage of the LCD segment RMS voltage close to the LCD threshold voltage.The RMS voltage calculated above can be controlled by dividing the LCD driving time ( control period) into two parts :

1. Active Time

2. Dead Time

[0017] The LCD driving waveforms are generated by using a software algorithm. During the Active time, the segment lines and COM lines are used to drive the LCD. During Dead time Segment and COM lines are used to control the LCD RMS voltage. The LCD RMS voltage is controlled by varying the timing of dead phase as shown in the LCD timing diagram. Thus, LCD RMS voltage can be adjusted to the optimal value depending up on the operating voltage of the LCD used and the temperature.

[0018] Dead time can be used to decrease Vrms as well as to increase it (on controller with small supply voltage). Dead time is a voltage compensation time to regulate the rms voltage up and down. The dead time control technique is independent of LCD multiplexing method (Duplex, Quadruplex...) and bias voltage technique ( ½ bias, 1/3 bias...). Dead time can be implemented after each "control period" or after each end of frame depending up on quality of the LCD and frequency of the frame to avoid flickering effect on LCD. The Controller of LCD pattern + Dead time could be a microcontroller or any kind of ASIC.

[0019] Each frame period consists of four control periods( for quadruplex LCD), one control period per COM line. Each COM line generates its waveform during its corresponding control period e.g. COM1 line during (0- T/4). During other control periods COM1 remains at level Vdd/2. As mentioned above, each control period consists of two parts:

1. Active time

2. Dead time

[0020] During OC1, voltage Vdd is applied for the segments which have to be turned ON and 0 for the segments which have to be turned OFF. COM line which corresponds to this control period is set to low level. Other COM lines are set to level Vdd/2.

[0021] During OC2, all segments and COM lines are inactive(set to low level) if it is desired to decrease the Vrms( figure2) and COM lines are set low, segments lines are set high if is desired to increase the Vrms( figure3).

[0022] During OC3, Segment Lines are supplied with voltage levels which are inverted to the one applied during OC1. COM line which corresponds to this control period is set to high level. Other COM lines are set to level Vdd/2.

[0023] During OC4, all segments and COM lines are inactive(set to low level) if it is desired to decrease the Vrms and COM lines are set high, segments are set low if it is desired to increase the Vrms( figure3).

Where
T = Active Time
xT = Dead Time
x is a proportion of the dead time
Vx = Segment Voltage during the dead time

Since Vx = 0 ( incase of decrease of Rms Voltage, figure 2)
Putting Vx = 0, in the above equation.

[0024] In case of increase ofRms voltage , Vx = 0 for 3 dead periods and Vx = +/- Vdd for 5 dead periods( figure 3).

[0025] Putting the value for Vx ,

[0026] Since Vx = 0 ( incase of decrease of rms voltage, figure 2)

[0027] In case of increase of Rms voltage, Vx = 0 for 5 dead periods and Vx = +/- Vcc for 3 dead periods (figure 3). Putting the value for Vx ,

[0028] Figure 4 shows an implementation of the invention using a standard microcontroller.

[0029] LCD segment RMS voltage is controlled by controlling the timing for the waveforms driving the LCD segment and common lines. These controlled LCD driving waveforms are generated by using software driver.

[0030] An external 2 resistor bridge (per common line) is connected externally to the MCU I/O ports which are used for driving the LCD common lines. D.C. power supply of Vdd or Vcc is used for driving all the components of the device.

[0031] The LCD Timing is generated by using the timer interrupts( timer peripheral is available inside the microcontroller).

[0032] Active time starts after timer interrupt1 and dead time starts after timer interrupt2. Total 16 interrupts are generated in each frame period with four interrupts per control period. There are four events i.e. OC1, OC2, OC3, OC4 in each control period. Timing for OC1, OC3 are same and then for OC2, OC4 are same.

[0033] The Vdd/2 level is generated by the externally connected resistors.

[0034] Figure 5 shows the flowchart of the software used for the microcomputer implementation of Figure 4, Timer interrupt (5.1) triggers an OC1 event (5.2) that applies supply voltage Vdd for segments to be turned on and 0V for segment to be turned off (5.6) while the COM line for the selected period is set to low and other COM lines are tristated. The timer is reinitialized.

[0035] At the next timer interrupt (5.1) event OC2 is triggered (5.3). All segments and COM lines are set to 0V if a Vrms is to be decreased and segment are set high and COM lines low if Vrms is to be increased (5.7). The timer is reinitialized.

[0036] At the next timer interrupt event OC3 is triggered (5.4). Segment lines are supplied levels that are inverted with respect to those supplied during OC1. The COM line corresponding to these time slots set high, other COM lines are tristated (5.8). The timer is reinitialized.

[0037] The next timer interrupt triggers the OC4 event (5.5). All segment and COM lines are set low if Vrms is to be decreased. COM lines are set high and segments are set low if Vrms is to be increased (5.9). The timer is reinitialized.

[0038] The entire sequence is repeated continuously.

Claims

1. An LCD display driver for multiplex driving an LCD display having SEGMENT and COM lines, said display driver comprising:

- a COM line driver arranged to generate as many COM signals as the required multiplexing level of said display, and

- a SEGMENT line driver arranged to generate SEGMENT signals, so that every LCD segment experiences an AC voltage signal with an essentially zero DC component,

said LCD display driver arranged to provide adjustable contrast by generating said COM and said SEGMENT signals as signals, containing one or more active periods and one or more inactive periods, the relative time proportions of the active periods and the inactive periods being adjustable so as to control the RMS voltage across the LCD elements as desired, wherein:

a) during said active periods the SEGMENT and COM lines are used to drive said LCD display by :

- generating a waveform for each COM signal in a particular time slot of a signal frame containing multiple time slots for selecting in each time slot a particular COM line, and

- generating via said SEGMENT line driver active signals relative to the corresponding time-slot such that in the selected COM line the required display segments are turned-on while the remaining display segments are turned off, and

b) during said inactive periods, occurring in said signal frame, the SEGMENT and COM lines are used to decrease the RMS voltage level across the LCD elements as desired by adjusting the relative active time to inactive time for the COM signals,

characterized in that
said LCD display driver is arranged to generate, during said active periods, said COM-signals as signals, set to logic levels, including a high level (Vdd) and a low level (oV), or to a bias voltage level (Vdd/2), and said SEGMENT signals as signals, set to said logic levels, including said high level and said low level,
and said LCD display driver being arranged to set, during said inactive periods, the SEGMENT and COM signals to said logic levels, including said high level and said low level such that the the RMS voltage level across the LCD elements can be increased or decreased as desired.

2. An LCD driver as claimed in claim 1, wherein the required COM and SEGMENT signals are generated at the input-output pins of an ordinary microcontroller using software means.

3. An LCD driver as claimed in claim 1, wherein said LCD driver uses a bias voltage technique, wherein the bias voltage is provided by means of a resistor network across the COM signal lines while the COM signals are tristated.

4. An LCD driver as claimed in claim 1, wherein the RMS voltage level is adjusted to a higher or lower level depending upon the threshold voltage of the LCD display.

5. An LCD driver as claimed in claim 1, wherein the LCD driver is implemented as an ASIC.

6. An LCD driver as claimed in claim 1, wherein the inactive period is provided in each time slot.

7. An LCD driver as claimed in claim 1, wherein the inactive period is provided at the end of each frame.

8. A method for multiplex driving an LCD display having SEGMENT and COM lines, said method comprising the steps of:

- generating as many COM signals as the required multiplexing level of said display, and

- generating SEGMENT signals, so that every LCD segment experiences an AC voltage signal with an essentially zero DC component,

said method providing adjustable contrast by generating said COM and said SEGMENT signals as signals containing one or more active periods and one or more inactive periods, the relative time proportions of the active periods and the inactive periods being adjustable so as to control the RMS voltage across the LCD elements as desired, wherein:

a) during said active periods the SEGMENT and COM lines are used to drive said LCD display by:

- generating a waveform for each COM signal in a particular time slot of a signal frame containing multiple time slots for selecting in each time slot a particular COM line, and

- supplying active signals relative to the corresponding time-slot such that in the selected COM line the required display segments are turned-on while the remaining display segments are turned off, and

b) during said inactive periods, occurring in said signal frame, the SEGMENT and COM lines are used to decrease the RMS voltage level across the LCD elements as desired by, adjusting the relative active time to inactive time for the COM signals.

characterized by
generating, during said active periods, said COM signals as signals, set to logic levels, including a high level (Vdd) and a low level (oV), or to a bias voltage level (Vdd/2), and said SEGMENT signals as signals, set to said logic levels, including said high level and said low level, and by setting, during said inactive periods, the SEGMENT and COM signals to said logic levels, including said high level and said low level so as to increase or decrease the RMS voltage level across the LCD element as desired.

9. A method as claimed in claim 8, using a standard microcontroller.

10. A method as claimed in claim 8, wherein a bias voltage technique is used, wherein the biasing voltage is provided by using a resistor network across the COM signal line.

Ansprüche

1. LCD-Anzeige-Treiber zum Multiplex-Ansteuern einer LCD-Anzeige mit SEGMENT- und COM-Leitungen, wobei der Anzeige-Treiber umfasst:

- einen COM-Leitungs-Treiber, eingerichtet zum Erzeugen so vieler COM-Signale, wie es dem benötigten Multiplex-Level der Anzeige entspricht, und

- einen SEGMENT-Leitungs-Treiber, eingerichtet zum Erzeugen von SEGMENT-Signalen, so dass jedes LCD-Segment ein Wechselspannungssignal mit einer im wesentlichen verschwindenden Gleichkomponente erhält,
wobei der LCD-Anzeige-Treiber eingerichtet ist, einen einstellbaren Kontrast durch Erzeugen der COM- und SEGMENT-Signale als eine oder mehrere aktive Perioden und eine oder mehrere inaktive Perioden umfassende Signale vorzusehen, wobei die relativen Zeitverhältnisse der aktiven Perioden und der inaktive Perioden einstellbar sind, um so die RMS-Spannung über den LCD-Elementen wie gewünscht zu steuern, wobei

a) die SEGMENT- und COM-Leitungen während der aktiven Perioden benutzt werden, um die LCD-Anzeige anzusteuern durch

- Erzeugen einer Wellenform für jedes COM-Signal in einem bestimmten Zeitschlitz eines Signalrahmens mit mehreren Zeitschlitzen zum Auswählen einer besonderen COM-Leitung in jedem Zeitschlitz, und

- Generieren aktiver Signale über den SEGMENT-Leitungstreiber relativ zu dem entsprechenden Zeitschlitz, so dass auf der selektierten COM-Leitung die erforderlichen Anzeige-Segmente eingeschaltet sind, während die übrigen Anzeigesegmente abgeschaltet sind, und

b) die SEGMENT-und COM-Leitungen während der in dem Signalrahmen auftretenden inaktiven Perioden durch Einstellen der relativen aktiven Zeit im Verhältnis zur inaktiven Zeit für die COM-Signale wie gewünscht zum Vermindern des RMS-Spannungspegels über den LCD-Elementen verwendet werden,

dadurch gekennzeichnet, dass
der LCD-Anzeige-Treiber eingerichtet ist, während der aktiven Perioden die COM-Signale als Signale zu erzeugen, die auf Logikpegel einschließlich eines hohen Pegels (V_dd) und eines niedrigen Pegels (0V) oder als auf einen Vorspannungspegel (V_dd/2) eingestellt sind, und die SEGMENT-Signale als Signale zu erzeugen, die auf Logikpegel einschließlich des hohen Pegels und des niedrigen Pegels eingestellt sind, und
wobei der LCD-Anzeige-Treiber eingerichtet ist, während der inaktiven Perioden die Segment- und COM-Signale auf die Logikpegel einschließlich eines hohen Pegels sowie eines niedrigen Pegel einzustellen, so dass der RMS-Spannungspegel über den LCD-Elementen wie gewünscht erhöht oder vermindert werden kann.

2. LCD-Treiber nach Anspruch 1, wobei die benötigten COM- und SEGMENT-Signale unter Verwendung von Software-Einrichtungen an den Eingangs-/Ausgangs-Anschlüssen eines gewöhnlichen Mikrocontrollers erzeugt werden.

3. LCD-Treiber nach Anspruch 1, wobei der LCD-Treiber eine Vorspannungstechnik benutzt, wobei die Vorspannung mittels eines WiderstandsNetzwerkes über die COM-Signalleitungen geliefert wird, während die COM-Signale gemäß einem Dreizustands-Schema eingestellt sind.

4. LCD-Treiber nach Anspruch 1, wobei der RMS-Spannungspegel in Abhängigkeit von der Schwellenspannung der LCD-Anzeige auf einen höheren oder niedrigeren Pegel eingestellt wird.

5. LCD-Treiber nach Anspruch 1, wobei der LCD-Treiber als ein ASIC implementiert ist.

6. LCD-Treiber nach Anspruch 1, wobei die inaktive Periode im Zeitschlitz vorgesehen ist.

7. LCD-Treiber nach Anspruch 1, wobei die inaktive Periode am Ende jedes Rahmens vorgesehen ist.

8. Verfahren zum Multiplex-Ansteuern einer LCD-Anzeige mit SEGMENT- und COM-Leitungen, wobei das Verfahren folgende Schritte umfasst:

- Erzeugen so vieler COM-Signale, wie es dem Multiplex-Level der Anzeige entspricht, und

- Erzeugen von SEGMENT-Signalen, so dass jedes LCD-Segment ein Wechselspannungssignal mit einer im wesentlichen verschwindenden Gleichkomponente erhält,
wobei das Verfahren durch Erzeugen der COM- und der SEGMENT-Signale als Signale, die eine oder mehrere aktive Perioden und eine oder mehrere inaktive Perioden beinhalten, einen einstellbaren Kontrast vorsieht, wobei die relativen Zeitverhältnisse der aktiven Perioden und der inaktiven Perioden einstellbar sind, um so die RMS-Spannung über den LCD-Elementen wie gewünscht zu steuern, wobei

a) die SEGMENT- und COM-Leitungen während der aktiven Perioden zum Ansteuern der LCD-Anzeige verwendet werden durch

- Erzeugen einer Wellenform für jedes COM-Signal in einem bestimmten Zeitschlitz eines mehrere Zeitschlitze aufweisenden Signalrahmens zum Selektieren einer bestimmten COM-Leitung in jedem Zeitschlitz, und

- Liefern aktiver Signale relativ zu dem entsprechenden Zeitschlitz derart, dass in der selektierten COM-Leitung die benötigten Anzeigesegmente eingeschaltet sind, während die verbleibenden Anzeigesegmente abgeschaltet sind, und

b) die SEGMENT- und COM-Leitungen während der inaktiven Perioden, die in dem Signalrahmen auftreten, verwendet werden, um den RMS-Spannungspegel über den LCD-Elementen durch Einstellen der relativen aktiven Zeit im Verhältnis zur inaktiven Zeit für die COM-Signale wie gewünscht zu vermindern,

gekennzeichnet durch
Erzeugen der COM-Signale während der aktiven Perioden als Signale, die auf Logikpegel einschließlich eines hohen Pegels (V_dd) und einschließlich eines niedrigen Pegels (0V) oder auf einen Vorspannungspegel (V_dd/2), eingestellt sind, sowie Erzeugen der SEGMENT-Signale als Signale, die auf die Logikpegel einschließlich des hohen Pegels und des niedrigen Pegels eingestellt sind, und Einstellen der SEGMENT- und COM-Signale während der inaktiven Perioden auf die Logikpegel mit dem hohen Pegel und dem niedrigen Pegel, um so den RMS-Spannungspegel über den LCD-Elementen wie gewünscht zu erhöhen oder zu vermindern.

9. Verfahren nach Anspruch 8, einen Standard-Mikrocontroller verwendend.

10. Verfahren nach Anspruch 8, wobei eine Vorspannungstechnik verwendet wird, wobei die Vorspannung durch Verwendung eines Widerstandsnetzwerkes über der COM-Signalleitung geliefert wird.

Revendications

1. Pilote d'afficheur à cristaux liquides pour entraînement multiplex d'un afficheur à cristaux liquides ayant des lignes SEGMENT et COM, ledit pilote d'afficheur comprenant :

- un pilote de ligne COM agencé pour générer autant de signaux COM que le niveau de multiplexage requis dudit afficheur, et

- un pilote de ligne SEGMENT agencé pour générer des signaux SEGMENT, de sorte que chaque segment à cristaux liquides subit un signal de tension alternative avec une composante continue essentiellement nulle,

ledit pilote d'afficheur à cristaux liquides étant agencé pour fournir un contraste réglable en générant lesdits signaux COM et lesdits signaux SEGMENT en tant que signaux, contenant une ou plusieurs périodes actives et une ou plusieurs périodes inactives, les proportions de temps relatives des périodes actives et des périodes inactives étant réglables, de façon à commander la tension efficace aux bornes des éléments à cristaux liquides comme souhaité, dans lequel :

a) pendant lesdites périodes actives, les lignes SEGMENT et COM sont utilisées pour piloter ledit afficheur à cristaux liquides par :

- génération d'une forme d'onde pour chaque signal COM dans une tranche de temps particulière d'une trame de signal contenant de multiples tranches de temps permettant de sélectionner dans chaque tranche de temps une ligne COM particulière,
et

- génération via ledit pilote de ligne SEGMENT de signaux actifs relatifs à la tranche de temps correspondante de sorte que dans la ligne COM sélectionnée les segments d'afficheur requis sont activés tandis que les segments d'afficheur restants sont désactivés, et

b) pendant lesdites périodes inactives, se produisant dans ladite trame de signal, les lignes SEGMENT et COM sont utilisées pour diminuer le niveau de tension efficace aux bornes des éléments à cristaux liquides comme souhaité en réglant le temps actif relatif au temps inactif pour les signaux COM,

caractérisé en ce que
ledit pilote d'afficheur à cristaux liquides est agencé pour générer, pendant lesdites périodes actives, lesdits signaux COM en tant que signaux, établis aux niveaux logiques, comprenant un niveau élevé (Vdd) et un niveau faible (oV), ou à un niveau de tension de polarisation (Vdd/2), et lesdits signaux SEGMENT en tant que signaux, établis auxdits niveaux logiques, incluant ledit niveau élevé et ledit niveau faible,
et ledit pilote d'afficheur à cristaux liquides étant agencé pour établir, pendant lesdites périodes inactives, les signaux SEGMENT et COM auxdits niveaux logiques, incluant ledit niveau élevé et ledit niveau faible, de sorte que le niveau de tension efficace aux bornes des éléments à cristaux liquides peut être augmenté ou diminué comme souhaité.

2. Pilote à cristaux liquides selon la revendication 1, dans lequel les signaux COM et SEGMENT souhaités sont générés au niveau des broches d'entrée/de sortie d'un microcontrôleur ordinaire utilisant des moyens logiciels.

3. Pilote à cristaux liquides selon la revendication 1, dans lequel ledit pilote à cristaux liquides utilise une technique de tension de polarisation, dans lequel la tension de polarisation est fournie au moyen d'un réseau de résistances aux bornes des lignes de signaux COM tandis que les signaux COM sont mis en trois états.

4. Pilote à cristaux liquides selon la revendication 1, dans lequel le niveau de tension efficace est réglé à un niveau plus élevé ou plus faible selon la tension seuil de l'afficheur à cristaux liquides.

5. Pilote à cristaux liquides selon la revendication 1, dans lequel le pilote à cristaux liquides est implémenté comme un ASIC.

6. Pilote à cristaux liquides selon la revendication 1, dans lequel la période inactive est fournie dans chaque tranche de temps.

7. Pilote à cristaux liquides selon la revendication 1, dans lequel la période inactive est fournie à la fin de chaque trame.

8. Procédé de pilotage multiplex d'un afficheur à cristaux liquides comportant des lignes SEGMENT et COM, ledit procédé comprenant les étapes de :

- génération d'autant de signaux COM que le niveau de multiplexage requis dudit afficheur, et

- génération de signaux SEGMENT, de sorte que chaque segment à cristaux liquides subit un signal de tension alternative avec une composante continue essentiellement nulle,

ledit procédé fournissant un contraste réglable en générant lesdits signaux COM et lesdits signaux SEGMENT en tant que signaux, contenant une ou plusieurs périodes actives et une ou plusieurs périodes inactives, les proportions de temps relatives des périodes actives et des périodes inactives étant réglables, de façon à commander la tension efficace aux bornes des éléments à cristaux liquides comme souhaité, dans lequel :

a) pendant lesdites périodes actives, les lignes SEGMENT et COM sont utilisées pour piloter ledit afficheur à cristaux liquides par :

- génération d'une forme d'onde pour chaque signal COM dans une tranche de temps particulière d'une trame de signal contenant de multiples tranches de temps permettant de sélectionner dans chaque tranche de temps une ligne COM particulière, et

- fourniture de signaux actifs relatifs à la tranche de temps correspondante de sorte que dans la ligne COM sélectionnée les segments d'afficheur requis sont activés tandis que les segments d'afficheur restants sont désactivés, et

b) pendant lesdites périodes inactives, se produisant dans ladite trame de signal, les lignes SEGMENT et COM sont utilisées pour diminuer le niveau de tension efficace aux bornes des éléments à cristaux liquides comme souhaité en réglant le temps actif relatif au temps inactif pour les signaux COM,

caractérisé par
la génération, pendant lesdites périodes actives, desdits signaux COM en tant que signaux, établis aux niveaux logiques, comprenant un niveau élevé (Vdd) et un niveau faible (oV), ou à un niveau de tension de polarisation (Vdd/2), et desdits signaux SEGMENT en tant que signaux, établis auxdits niveaux logiques, incluant ledit niveau élevé et ledit niveau faible, et en établissant, pendant lesdites périodes inactives, les signaux SEGMENT et COM auxdits niveaux logiques, incluant ledit niveau élevé et ledit niveau faible, de façon à augmenter ou diminuer le niveau de tension efficace aux bornes des éléments à cristaux liquides comme souhaité.

9. Procédé selon la revendication 8, utilisant un microcontrôleur type.

10. Procédé selon la revendication 8, dans lequel une technique de tension de polarisation est utilisée, dans lequel la tension de polarisation est fournie en utilisant un réseau de résistances aux bornes de la ligne de signaux COM.

Drawing